1. Field of the Invention
The present invention relates to an ignition timing control device for internal-combustion engines such as gasoline engines and diesel engines and, more particularly, to an ignition timing control device for internal-combustion engines which controls what is called knocking phenomenon caused by abnormal combustion in a combustion chamber of the internal-combustion engine and producing abnormal sound and abnormal vibration in the vicinity of a cylinder block.
2. Description of the Prior Art
Generally, the internal-combustion engine, especially the internal-combustion engine for motor vehicles, produces driving power by reciprocating pistons with combustion pressures created by the ignition by a spark discharged from a spark plug, explosion and burning of an air-fuel mixture drawn into, and compressed in, a cylinder of this engine. Therefore, to obtain a maximum effective motive power it is necessary to control the ignition timing such that aforesaid combustion pressures may constantly be kept at a maximum. To obtain the maximum combustion pressure, the ignition timing must to be controlled to optimize the timing that the spark plug ignites to burn the air-fuel mixture in the combustion chamber.
FIG. 1 shows a conventional ignition timing control device in an internal-combustion engine, in which a numeral 1 designates an acceleration sensor installed in the engine for sensing the vibratory acceleration of the engine; 2 a frequency filter which allows the passage of such high-frequency components of a signal outputted from the acceleration sensor that are sensitive to knocking; 3 an analog gate which shuts off noise of the output signal coming through the frequency filter 2 that acts as a disturbance wave to knock sensing; 4 a gate timing controller which controls the opening and closing of the analog gate 3 correspondingly to the timing of disturbance noise ocurrence; 5 a noise level detector which detects the level of mechanical vibration noise of engine other than the knocking; 6 a comparator which compares the output voltage of the analog gate 3 with that of the noise level detector 5, and produces a knock detection pulse; 7 an integrator which integrates the output pulse of the comparator 6 and produces an integral voltage in accordance with knocking strength; 8 a phase shifter which shifts the phase of a reference ignition signal in accordance with the output voltage of the integrator 7; 9 a rotation signal gnerator which generates an ignition signal in accordance with an ignition-advance characteristic preset on the basis of the rotation of the engine output shaft; 10 a waveform shaping circuit which corrects the waveform of the output of the rotation signal generator 9 and, at the same time, controls the circuit closing angle of an ignition coil 12; and 11 a switching circuit which interrupts the current flow to the ignition coil 12 in accordance with the output signal of the aforementioned phase shifter 8.
FIG. 2 shows the frequency characteristics of the output signal of the acceleration sensor 1. The dotted line A indicates a signal waveform where no knocking takes place, while the full line B shows a signal waveform where the knocking takes place. The output signal of the acceleration sensor 1 includes, besides a knock signal (a signal generated with knocking), a mechanical noise of engine and various noise components coming in a signal transmission path, for example an ignition noise. From a result of a comparison between the dotted line A and the full line B in FIG. 2, it is understood that the knock signal has a peculiar frequency characteristic. Therefore, its distribution definitely differs, in each case, with the presence of knocking although it varies with a difference between engines or with a difference in the mounting position of the acceleration sensor 1. It, therefore, is possible to control the noise of other frequency components by filtering the frequency components of this knock signal, by sensing the knock signal efficiently.
FIGS. 3 and 4 shown the operation waveform of each part of a conventional device; FIG. 3 shows a mode in which no knocking is taking place, while FIG. 4 shows a mode in which the knocking is taking place. Referring to these FIGS. 3 and 4, the operation of the conventional device will be described. As the engine output shaft rotates, an ignition signal produced from the rotation signal generator 9 correspondigly to the preset ignition timing characteristics is shaped to an opening/closing pulse having a desired circuit closing angle by the waveform shaping circuit 10, and the switching circuit 11 is driven through the phase shifter 8 to interrupt the current flow to the ignition coil 12. The engine is ignited to operate by the ignition voltage of the ignition coil 12 that is built up as the flow of current is interrupted. Engine vibration occurring during the operation of this engine is sensed by the acceleration sensor 1.
Where no engine knocking is occurring, there takes place no engine vibration likely to be caused by knocks. However, since there occurs other mechanical vibration, a mechanical noise and an ignition noise affecting the signal transmission path during the ignition timing F will occur with the output signal of the acceleration sensor 1 as shown in FIG. 3 (a).
When this signal passes through the frequency filter 2, most of mechanical noise components are removed as shown in FIG. 3 (b). The ignition noise components, however, being powerful, will in some cases be outputted at a great level even after passing through the frequency filter 2. The ignition noise, if allowed to pass through the filter, will be mistaken as a knock signal; to prevent this, therefore, the analog gate 3 will close for a certain period after the ignition timing on a signal outputted from the gate timing controller 4 shown in FIG. 3(c) which is triggered by the output of the phase shifter 8, thus shutting off the ignition noise. With the output of the analog gate 3, only such a low-level mechanical noie as is shown by the waveform C in FIG. 3(d) will remain.
On the other hand, the noise level sensor 5 operates in response to changes of a peak value of the output signal of the analog gate 3. In this case, the noise level sensor 5 has a characteristic to be able to respond to relatively gentle changes of the peak value of ordinary mechanical noise, producing a direct current (DC) voltage slightly higher than the peak value of the mechanical noise (waveform D in FIG. 3(d)).
Therefore, since the output of the noise level sensor 5 is greater than a mean peak value of an output signal of the analog gate 3 as shown in FIG. 3 (d), the comparator 6 which compares these will not output any noise signal; that is, the noise signal is thoroughly removed.
Therefore, the output voltate of the integrator 7 remains zero as shown in FIG. 3 (f), and accordingly the phase shifting angle (a difference in the input and output phases in FIG. 3(g), (h)) by the phase shifter 8 will also become zero.
Therefore, the opening closing phase of the switching circuit 11 which is driven by this output, that is, the current interruption phase of the ignition coil 12, will become of the same phase as the reference ignition signal of the output of the waveform shaping circuit 10. The ignition timing, therefore, will become the reference ignition timing.
When knocking occurs, a knock signal is included in the output of the acceleration sensor 1 near a point retarded for a certain time from the ignition timing as shown in FIG. 4 (a), and, after passing through the frequency filter 2 and the analog gate 3, will become a mechanical noise largely overlapped by a knock signal as shown at the waveform C in FIG. 4(d).
Of the signal that has passed through this analog gate 3, the knock signal rises sharply; therefore the level of the output voltage of the noise level sensor 5 retards to respond to the knock signal. In consequence, since the input of the comparator 6 becomes as indicated by the waveforms C and D in FIG. 4 (d) respectively, a pulse will occur with the output of the comparator 6 as shown in FIG. 4 (e).
The integrator 7 integrates the pulse, producing an integrated voltage as shown in FIG. 4 (f). Since the phase shifter 8 shifts the output signal (reference ignition signal shown in FIG. (g) of the waveform shaping circuit 10) to the time-delay side in accordance with the output voltage of the integrator 7, the output phase of the phase shifter 8 is delayed behind the phase of the reference ignition signal of the waveform shaping circuit 10, and actuates the switching circuit 11 by a phase shown in FIG. 4 (h). Consequently, the ignition timing is delayed, thus controlling knocking tendencies. As a result, the conditions shown in FIGS. 3 and 4 are repeated to perform the optimum ignition timing control.
Since the conventional device is so constituted as described above, the decreased speed (the speed at which the ignition timing moves toward the reference until it is reset on the spark advance side) of the integrator 7 indicates the characteristic of a unit of a second per degree of rotation angle of the engine output shaft, which is a large time constant. This decreased speed prevents the occurrence of severe knocks by controlling the too fast return of the ignition timing toward the spark advance side and suddenly into the knocking region. This is an important characteristic for ignition timing control.
Therefore, to determine the amount of knocks sensed per knock sensing from the output of this integrator 7, it is necessary to obtain the output of the aforementioned integrator 7 immediately before and immediately after the knock sensing and to determine a difference between values thus obtained, that is, an output variation of the integrator 7 per knock sensing. This requires complicated calculation. Only reading the value indicated on this integrator 7 at the time of knock sensing, however, is not enough to obtain the amount of knocking sensed. Therefore, it is because the output of the integrator 7, for example before the occurrence of knocking, must be memorized and, in the event that the knocking has taken place, a difference between the output of the integrator 7 immediately before the occurrence of knocking and that immediately after the occurrence of knocking must be obtained.
In the meantime, the technological level of engine control has a trend to become more and more enhanced; in a multicylinder engine, engine control is accurately effected for each cylinder to maintain all the cylinders in a much more improved combustion state in order to provide an improved engine output. To insure such control, it is necessary to detect and determine the amount of knocking occurring in each cylinder. However, the conventional device has such a problem that a complicated calculation is needed to determine the amount of knocking occurrence every time the knocking occurs from the output of the integrator 7, and besides a much larger-scale circuit is needed to determine the amount of knocking occurrence for each cylinder from this.
Furthermore, a knock signal produced corresponding to the occurrence of knocking in the engine can not be sensed unless a knock signal and a noise signal in the output of the frequency filter (FIGS. 3 (b) and 4 (b)) can be discriminated by a voltage value. Viewed with respect to the vibration characteristics of an engine, the conventional device has the following problem that a noise signal like a knock signal sometimes occurs in for example an engine that has undergone a durability test; this noise signal in some cases causes the ignition timing control device to make a wrong operation. Namely, during an initial period (when the engine is still new), the control device operates as desired, but with the lapse of operating time, the noise signal grows and is incorrectly sensed, resulting in such troubles as an inefficiently controlled ignition timing, lowered engine output, increased fuel consumption, and an exhaust gas temperature rise.